As mobile devices have been increasingly developed, and the demand for such mobile devices has increased, the demand for batteries has also sharply increased as an energy source for the mobile devices. Also, much research on batteries satisfying various needs has been carried out.
In terms of the shape of batteries, the demand for prismatic secondary batteries or pouch-shaped secondary batteries, which are thin enough to be applied to products, such as mobile phones, is very high. In terms of the material for batteries, the demand for lithium secondary batteries, such as lithium ion batteries and lithium ion polymer batteries, having high energy density, high discharge voltage, and high output stability, is very high.
Furthermore, secondary batteries may be classified based on the construction of an electrode assembly having a cathode/separator/anode structure. For example, the electrode assembly may be constructed in a jelly-roll (winding) type structure in which long-sheet type cathodes and anodes are wound while separators are disposed respectively between the cathodes and the anodes, a stacking type structure in which pluralities of cathodes and anodes having a predetermined size are successively stacked one on another while separators are disposed respectively between the cathodes and the anodes, or a stacking/folding type structure in which pluralities of cathodes and anodes having a predetermined size are successively stacked one on another while separators are disposed respectively between the cathodes and the anodes to constitute a bi-cell or a full-cell, and then the bi-cell or the full-cell is wound.
Recently, much interest has been taken in a pouch-shaped battery constructed in a structure in which such a stacking or stacking/folding type electrode assembly is mounted in a pouch-shaped battery case made of an aluminum laminate sheet because of low manufacturing costs, light weight, and easy modification in shape. As a result, the use of the pouch-shaped battery has gradually increased.
FIG. 1 is an exploded perspective view typically illustrating the general structure of a conventional representative pouch-shaped secondary battery 10.
Referring to FIG. 1, the pouch-shaped secondary battery 10 includes an electrode assembly 30, pluralities of electrode taps 40 and 50 extending from the electrode assembly 30, electrode leads 60 and 70 welded to the electrode taps 40 and 50, respectively, and a battery case 20 for receiving the electrode assembly 30.
The electrode assembly 30 is a power generating element comprising cathodes and anodes successively stacked one on another while separators are disposed respectively between the cathodes and the anodes. The electrode assembly 30 is constructed in a stacking structure or a stacking/folding structure. The electrode taps 40 and 50 extend from corresponding electrode plates of the electrode assembly 30. The electrode leads 60 and 70 are electrically connected to the electrode taps 40 and 50 extending from the corresponding electrode plates of the electrode assembly 30, respectively, for example, by welding. The electrode leads 60 and 70 are partially exposed to the outside of the battery case 20. To the upper and lower surfaces of the electrode leads 60 and 70 is partially attached insulative film 80 for improving sealability between the battery case 20 and the electrode leads 60 and 70 and, at the same time, for securing electrical insulation between the battery case 20 and the electrode leads 60 and 70.
The battery case 20 is made of an aluminum laminate sheet. The battery case 20 has a space defined therein for receiving the electrode assembly 30. The battery case 20 is formed generally in the shape of a pouch. In the case that the electrode assembly 30 is a stacking type electrode assembly as shown in FIG. 1, the inner upper end of the battery case 20 is spaced apart from the electrode assembly 30 such that the plurality of cathode taps 40 and the plurality of anode taps 50 can be coupled to the electrode leads 60 and 70, respectively.
FIG. 2 is an enlarged view, in section, illustrating the inner upper end of the battery case of the secondary battery shown in FIG. 1, in which the cathode taps are coupled to each other in a concentrated state and connected to the cathode lead, and FIG. 3 is a front see-through view illustrating the secondary battery of FIG. 1 in an assembled state.
Referring to these drawings, the plurality of cathode taps 40, which extend from cathode collectors 41 of the electrode assembly 30, are connected to one end of the cathode lead 60, for example, in the form of a welded bunch constituted by integrally combining the cathode taps 40 with each other by welding. The cathode lead 60 is sealed by the battery case 20 while the other end 61 of the cathode lead 60 is exposed to the outside of the battery case 20. Since the plurality of cathode taps 40 are integrally combined with each other to constitute the welded bunch, the inner upper end of the battery case 20 is spaced a predetermined distance from the upper end surface of the electrode assembly 30, and the cathode taps 40 combined in the form of the welded bunch are bent approximately in the shape of V. Accordingly, the coupling regions between the electrode taps and the corresponding electrode leads may be referred to as “V-form regions.”
However, such V-form regions have a problem in the aspect of safety of the battery. When the battery drops with the upper end of the battery, i.e., the cathode lead 60 of the battery, down, or an external physical force is applied to the upper end of the battery, the electrode assembly 30 moves toward the inner upper end of the battery case 20, or the upper end of the battery case 20 is crushed. As a result, the anode of the electrode assembly 30 is brought into contact with the cathode taps 42 or the cathode lead 60, and therefore, short circuits may occur inside the battery. Consequently, the safety of the battery is greatly lowered.
Accordingly, there has been proposed a secondary battery constructed in a structure in which a predetermined region of the battery case corresponding to the upper end interface of the electrode assembly in the battery is modified into a specific form according to the present invention as a solution of fundamentally solving the above-mentioned problem.
In this connection, there has been known some technologies for forming a groove in one surface of the battery case. As an example, Japanese Patent Registration No. 3730981 discloses a secondary battery constructed in a structure in which a plurality of convex parts are formed at least one surface of the battery case surrounding the electrode assembly to improve heat dissipation, and the convex parts are filled with fillers. This technology has an advantage in that the film surface area of the battery case is increased by the plurality of convex parts with the result that the heat dissipation is increased, and the shape of the convex parts is stably maintained by the fillers in the convex parts. However, it is not possible to prevent the occurrence of an internal short circuit of the battery due to the upward movement of the electrode assembly when an external force is applied to the electrode taps of the electrode assembly.
As another example, Japanese Patent Application Publication No. 2001-057179 a secondary battery constructed in a structure in which grooves or convex parts are formed at least one surface of the battery case in the form of an X-shape linear pattern so as to restrain the expansion of the battery case and thus prevent the deformation of the battery case. As clearly described in the specification of the publication, the intersecting lines structurally serve as crossbeams to increase the total strength of the battery case, thereby prevent the deformation of the battery case due to the expansion of the battery case. However, this technology has a problem in that a desired effect is accomplished only when the linear pattern is formed in the X shape. Also, this technology has another problem in that a desired effect is accomplished only when the battery case is a metal container, and therefore, satisfactory results are not obtained when the battery case is a sheet-type battery case. In addition, it is required that the linear pattern be formed very deeply so as to structurally accomplish the crossbeam effect. However, this process may greatly deteriorate the mechanical strength of the battery case at the intersection region of the lines.
Consequently, there is high necessity for a technology that is capable of preventing the occurrence of a short circuit of the secondary battery due to the movement of the electrode assembly without difficulty in a manufacturing process.